The present invention relates to a fuel injection control method and a system for a cylinder-inside direct injection type spark ignition internal combustion engine, and more particularly to a control method and system for controlling the duration of an injection period at low engine-speeds and heavy engine loading.
Japanese Patent Provisional Publication No. 8-193536 discloses a cylinder-inside direct injection type spark ignition internal combustion engine. In this publication, fuel injection is carried out by setting an injection pulse width at the engine start-up timing and suitably setting the fuel injection timing, in accordance with the coolant temperature at engine start-up.
However, in such a conventional engine, the fuel is highly pressurized by a high pressure fuel pump driven either by a camshaft or a crankshaft of the engine and injected from a fuel injector valve into an associated cylinder. Therefore, the fuel pressure is lowered because of the influence of injection during the engine start-up period, especially when the engine temperature is low. A long fuel injection period is required, however, the injection pulse width is determined in accordance with the fuel pressure at the injection start-up timing. Consequently, the effective injection amount per unit time becomes less due to a drop in the pressure so that the actual injection amount decreases, thereby degrading the engine starting operability Also, the response characteristics of the control procedure is limited in such conventional systems even when a fuel pressure sensor is provided, and therefore, it is difficult to timely consider the lowering of the fuel pressure at the injection detected during fuel injection to adjust the control. In other words, once a fuel injection rate has been determined and applied to an injector, it is difficult to adjust or extend the injection period during injection.